The present invention relates to a process for the oligomerization of alpha olefins. More specifically, the present invention relates to the preparation of alpha olefin oligomers having predominantly terminal unsaturation using a catalyst system comprising an alkyl aluminum halide component and a second component comprising at least one zirconium compound, preferably in combination with at least one titanium compound.
It is known in the art that alpha olefins are typically oligomerized using an acidic catalyst, normally either a Bronsted or Lewis acid. The oligomeric products derived from such acid-catalyzed oligomerization have mostly internal double bonds. These products also have a highly branched structure, due to isomerization side reactions.
In the presence of transition metal catalysts of the Ziegler-Natta type, alpha olefins generally polymerize to high molecular weight solid materials which are highly stereoregular. The preparation of a low molecular weight atactic polypropylene has been reported in the literature, however, employing a transition metal complex as a catalyst.
Hence, British Pat. No. 1,231,299 describes a process for preparing a low molecular weight atactic polypropylene using a catalyst system containing an alkoxy titanium trichloride and a dialkyl aluminum chloride. This process provides a highly regular oligomeric product resulting from mostly head-to-tail addition of monomer units. However, as in acid-catalyzed oligomerization, the double bond in this material is also internal.
Belgian Pat. No. 756,033 describes a process for converting ethylene to a mixture of linear alpha olefins having 4 to 40 carbon atoms, using a transition metal catalyst. The reaction product also contains high molecular weight solid polyethylene. The catalyst employed in this process comprises an alkyl aluminum halide and a zirconium complex, such as zirconium alkoxide, alkoxy zirconium halide, zirconium alkylamine and alkylamino zirconium halide.